The present invention relates to a receiving device for angle-modulated signals, in particular a receiving device which also carries out a selection of a desired transmission channel.
In cordless digital communications systems, for example DECT (Digital Enhanced Cordless Telecommunications), WDCT (Worldwide Digital Cordless Telecommunications), Bluetooth, SWAP (Shared Wireless Access Protocol) or WLAN (Wireless Local Area Network) radio systems, suitable receivers are required for a wireless reception of the transmitted radio-frequency signals. The receivers must be suitable for processing the type of digital modulation which is used in the relevant communications system, wherein the invention also relates to the field of frequency modulation.
Along with high sensitivity, a high level of integration, low costs, low power consumption and flexibility in terms of applicability in different digital communications systems are required in this respect.
In cordless digital communications systems, superheterodyne receivers are currently often used to receive and demodulate angle-modulated signals. xe2x80x9cLow-IFxe2x80x9d (Intermediate Frequency) or xe2x80x9cZero-IFxe2x80x9d (homodyne) receivers, which require no external filters to suppress mirror frequencies, are also increasingly used (for example in DECT mobile radio systems) to achieve high system integration and therefore lower system costs. Low-IF receivers use a relatively low intermediate frequency, which may, for example, be around 1 MHz in the case of input signal frequencies of around 2 GHz, whereas the intermediate frequency is 0 MHz in the case of zero-IF receivers. Analog FM (Frequency Modulation) demodulators based on the xe2x80x9climiter-discriminatorxe2x80x9d principle are currently used for demodulation in these receivers, whereby the baseband signal is initially reproduced and the transmitted symbols are subsequently detected using the baseband signal. The channel selection, i.e. the selection of the relevant required transmission channel of the receive signal, is carried out before the FM demodulation with the aid of analog filters, which filter out the unwanted frequency components or transmission channels. However, due to the analog circuit technology used in these receivers, these receivers are prone to the disadvantages associated with analog circuit technology, for example drift, ageing, temperature dependency, etc.
It is accordingly an object of the invention to provide a receiving device for angle-modulated signals which overcomes the above-mentioned disadvantages of the heretofore-known receiving devices of this general type and in which an effective channel selection and demodulation of an angle-modulated receive signal can be carried out.
With the foregoing and other objects in view there is provided, in accordance with the invention, a receiving device for angle-modulated signals, including:
an analog/digital converter device for converting an angle-modulated receive signal into a digitized receive signal;
a digital frequency conversion device provided downstream of the analog/digital converter device for converting the digitized receive signal into a baseband;
a digital channel selection device provided downstream of the digital frequency conversion device for selecting a receive signal component of a given transmission channel from the digitized receive signal; and
a digital demodulation device provided downstream of the digital channel selection device for demodulating the receive signal component selected by the digital channel selection device.
In other words, a receiving device for angle-modulated signals includes an analog/digital converter device provided for conversion of an angle-modulated receive signal into a digital signal, a digital frequency conversion device is provided downstream of the analog/digital converter device for conversion of the digitized receive signal into the baseband, a digital channel selection device is provided downstream of the digital frequency conversion device in order to select the receive signal component of a specific transmission channel from the digitized receive signal, and a digital demodulation device is provided downstream of the digital channel selection device for a demodulation of the selected receive signal component.
According to another feature of the invention, an analog frequency conversion device is provided upstream of the analog/digital converter device for converting the angle-modulated receive signal into an intermediate frequency band; and the digital frequency conversion device provided downstream of the analog/digital converter device is configured to convert the digitized receive signal from the intermediate frequency band into the baseband.
According to yet another feature of the invention, the analog frequency conversion device converts the angle-modulated receive signal having a carrier frequency into the intermediate frequency band having an intermediate frequency lower than the carrier frequency of the angle-modulated receive signal.
According to a further feature of the invention, the analog frequency conversion device converts the angle-modulated receive signal having a symbol rate into the intermediate frequency band having an intermediate frequency corresponding to the symbol rate of the angle-modulated receive signal.
According to another feature of the invention, the analog frequency conversion device converts the angle-modulated receive signal having a given channel spacing into the intermediate frequency band having an intermediate frequency corresponding to one half of the given channel spacing of the angle-modulated receive signal.
According to a further feature of the invention, a low-pass filter device is provided between the analog frequency conversion device and the analog/digital converter device for filtering the angle-modulated receive signal having been converted into the intermediate frequency band.
According to another feature of the invention, the analog/digital converter device, the digital frequency conversion device, and the digital channel selection device form a first signal processing path for processing an in-phase component of the angle-modulated receive signal and a second signal processing path for processing a quadrature component of the angle-modulated receive signal; and the digital demodulation device receives symbols output by the first signal processing path and symbols output by the second signal processing path for demodulation.
According to yet another feature of the invention, the analog/digital converter device includes a first analog/digital converter assigned to the first signal processing path, and a second analog/digital converter assigned to the second signal processing path; and the first analog/digital converter and the second analog/digital converter are configured as sigma-delta converters operating with oversampling.
According to an additional feature of the invention, the digital channel selection device includes a first digital channel selection unit assigned to the first signal processing path, and a second digital channel selection unit assigned to the second signal processing path.
According to another feature of the invention, the first and second channel selection units each have a multi-stage architecture with a plurality digital filters and with undersampling units provided alternately with the digital filters.
According to another feature of the invention, the first and second channel selection units each include a first digital filter, a first undersampling unit, a second digital filter, a second undersampling unit, a third digital filter and a third undersampling unit connected in series to one another.
According to a further feature of the invention, the first digital filter is a comb filter; the second digital filter is a bireciprocal lattice wave digital filter; and the third digital filter is a lattice wave digital filter.
According to another feature of the invention, the analog/digital converter device includes a first analog/digital converter assigned to the first signal processing path, and a second analog/digital converter assigned to the second signal processing path; the first analog/digital converter and the second analog/digital converter are configured as sigma-delta converters having a first filter order; and the first digital filter of the first and second digital channel selection units has a second filter order such that the second filter order is higher by a value of 1 than the first filter order.
According to another feature of the invention, the first and second analog/digital converters operate with a 32-fold oversampling; the first undersampling unit of the first and second channel selection units operates with an 8-fold undersampling; and the second and third undersampling units of the first and second channel selection units each operate with a 2-fold undersampling.
According to yet another feature of the invention, the first and second channel selection units each have an output side and each have an equalizer on the output side.
According to another feature of the invention, the digital filters of the first and second digital channel selection units are programmable digital filters with settable filter coefficients.
According to a further feature of the invention, the digital frequency conversion device is a digital complex multiplier.
According to yet a further feature of the invention, the digital complex multiplier is configured to access information stored in a table for performing a complex multiplication required for a frequency conversion into the baseband.
According to another feature of the invention, the digital complex multiplier is configured to apply a CORDIC (Coordinate Rotation Digital Computer) algorithm for performing a complex multiplication required for a frequency conversion into the baseband.
According to another feature of the invention, the analog/digital converter device, the digital frequency conversion device, and the digital channel selection device form a first signal processing path for processing an in-phase component of the angle-modulated receive signal and a second signal processing path for processing a quadrature component of the angle-modulated receive signal; the analog frequency conversion device includes a first frequency mixer assigned to the first signal processing path, and a second frequency mixer assigned to the second signal processing path; and the low-pass filter device includes a first low-pass filter assigned to the first signal processing path, and a second low-pass filter assigned to the second signal processing path.
According to yet another feature of the invention, the digital demodulation device includes a differential demodulator and a sign comparator provided downstream from the differential demodulator; and the differential demodulator outputs symbols, the sign comparator evaluates a sign of the symbols output by the differential demodulator in order to define a value of bits wherein the bits correspond to a selected one of the in-phase component of the receive signal and the quadrature component of the receive signal.
With the objects of the invention in view there is also provided, in a digital cordless communications system, a receiving device for angle-modulated signals, including:
an analog/digital converter device for converting an angle-modulated receive signal into a digitized receive signal;
a digital frequency conversion device provided downstream of the analog/digital converter device for converting the digitized receive signal into a baseband;
a digital channel selection device provided downstream of the digital frequency conversion device for selecting a receive signal component of a given transmission channel from the digitized receive signal; and
a digital demodulation device provided downstream of the digital channel selection device for demodulating the receive signal component selected by the digital channel selection device.
According to another feature of the invention, the digital cordless communications system is configured to transmit GFSK-modulated signals and the receiving device is configured to receive GFSK-modulated signals.
With the objects of the invention in view there is also provided, a method of receiving angle-modulated signals, the method includes the steps of:
converting, with an analog/digital converter device, an angle-modulated receive signal into a digitized receive signal;
converting, with a digital frequency conversion device provided downstream of the analog/digital converter device, the digitized receive signal into a baseband;
selecting, with a digital channel selection device provided downstream of the digital frequency conversion device, a receive signal component of a given transmission channel from the digitized receive signal; and
demodulating, with a digital demodulation device provided downstream of the digital channel selection device, the receive signal component selected by the digital channel selection device.
According to the invention, a digital channel selection is carried out. For this purpose, an angle-modulated receive signal is initially subjected to A/D conversion and transformed into the baseband. Digital channel selection is then carried out and, finally, digital demodulation and detection of the angle-modulated signal, for example a (G)FSK-modulated (Gaussian Frequency Shift Keying) signal.
Before the A/D conversion, a frequency conversion to a lower intermediate frequency can be carried out with subsequent low-pass filtering, a rough channel selection already being carried out through the use of the low-pass filtering.
Sigma-delta converters, operating at a specific oversampling rate, are preferably used as A/D converters. A digital complex multiplier can be used for frequency conversion into the baseband; this is implemented through the use of a stored table (xe2x80x9clook-up tablexe2x80x9d), or the use of a xe2x80x9cCORDICxe2x80x9d algorithm.
A series configuration including a plurality of alternately provided digital filters and undersampling stages is preferably used for the digital channel selection. This multi-stage architecture is essentially suitable for the digital cordless DECT, WDCT, Bluetooth, SWAP and WLAN communications systems due to their similar channel bandwidths in relation to the relevant symbol rates and the respective GFSK modulation which is used. A comb filter, a bireciprocal lattice wave digital filter, a further lattice wave digital filter and, finally, an equalizer are preferably used in this multi-stage digital channel selection architecture. The advantage of this architecture is that the undersampling or decimation required due to the sigma-delta converter which is preferably used for the A/D conversion is performed simultaneously with the channel selection.
A differential demodulator with a downstream sign comparator is preferably used as the digital demodulator and detector.
The receiving device according to the invention is essentially a digital configuration and therefore offers the generally known advantages of digital circuit technology, such as, in particular, no drift, no ageing, no temperature dependency and exact reproducibility. Furthermore, the digital receiving device can be configured as a programmable device, i.e. the characteristic of the channel selection filters can be adapted through the use of a suitable setting of the filter coefficients to the signal bandwidth present in a predefined cordless digital communications system.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a receiving device for angle-modulated signals, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.